(a) Field of the Invention
The present invention is related to a construction and manufacturing process of a carbon fiber paper, and more particularly, to a oxidized fiber needle-punched into an oxidized fiber felt, impregnated in low density resin, cured, and carbonized to avail the carbon fiber paper featuring high air permeability, low porosity, high flexure, and lower surface resistance.
(b) Description of the Prior Art
When compared to phosphoric acid fuel cell, the porous carbon electrode used by solid polymer fuel cell is highly demanded for its characteristics including gas and liquid diffusion, permeability, conductivity, strength, resilience, and durative compression strength. To seek a more compact size for the solid polymer fuel cell than that of the phosphoric acid fuel cell, the electrode must be made into a form of sheet or paper to reduce the volume of the cell.
To achieve the purpose, conventional paper making technology and method are currently adopted. Wherein, short carbon fibers are taken, and impregnated in thermally hardened resin during the curing process before the thermal treatment. However, thicker electrode used at the expense of resilience and comparatively higher porosity both contribute to damaged electrode when subject to pressure in the assembly of the cell. Furthermore, the conductivity is poor due to higher porosity among fibers and inconsistent due to uneven distribution of the fibers.
An improvement for the basic material for the porous carbonaceous electrode as disclosed in No. 7-142068(1995) Japanese patent involves mixing of carbonaceous milled fiber. However, the problem of lacking in resilience exists due to that the carbonaceous milled fiber is too thick to be applied in the solid polymer fuel cell.
No. 9-157052 (1997) Japanese patent discloses a manufacturing process for a porous carbon sheet; however, the conductivity of the electrode taught in the patent is very poor since its density is very low.
A basic material for porous carbon electrode that is resilient and highly conductive to be used in fuel cell and its manufacturing process disclosed in No. 489544 Taiwan patent (#6713034-2004 US Patent) adopts the wet paper making process. Wherein, short carbon fibers are first completely and consistently dispersed in the water before the addition of PVA short fibers serving as the adhesive for further complete and consistent dispersion to avail the carbon fiber paper by means of a sheet extrusion machine. The resultant paper is dipped in phenol resin, then pressed and cured to go through carbonization by batch within a temperature range of 1600˜2000° C. to come up with the finished product of porous carbon fiber paper. However, fibers on the finished paper are blamed for chaos in arrangement and orientation making it vulnerable to inadequate strength in the orientation vertical to the arrangement of the fibers.